Analgesics are used to control pain in various situations such as post surgical, post injury, cancer treatment, AIDS treatment and more. Analgesics used include steroidal, non-steroidal, opioid, and non-opioid analgesics. Many of these drugs have very short residence times in the body, ranging from 6 to 12 hours for steroids and non-steroids, to as low as 1 to 3 hours for opioids. Pain from the procedures described can last several days. These analgesics thus must be administered many times in order to be effective in controlling pain.
There are several methods for extending the time over which analgesics are effective. One is advanced chemical entities. Whereas analgesics such as morphine have a mean residence time of only a few hours, advanced synthetic analgesics such as OxyContin® have an effective residence time in the body of 8 hours. Some drawbacks to this material are the fact that it is orally delivered, and as a result the unit dose may be improperly modified by a patient, resulting in a dangerous overdose, or the patient may not be capable of swallowing the medication.
Another method for extending the effective time of analgesics is to meter them into the body via a trans-dermal patch. This method has the advantage of extending the release of analgesics to several days. The drawbacks to this method are that it is external to the body, and thus it may still be manipulated by the patient. For example, some of the patients are pets who scratch at and eat the patches. Another drawback is that the patches are both species and body weight specific. A patch used on a person cannot be used on a dog, and a dog patch may not be used on a cat. Different types of patches must be used for people of different body weights, etc.